The total surface area of refrigerant flow paths formed in a heat exchange pipe of a heat exchanger can be increased in a manner in which the diameter of each refrigerant flow path formed is decreased and the number of the refrigerant flow paths is increased in accordance with the decrease in the diameter. The decrease in the diameter of each refrigerant flow path enables the heat exchange performance of the heat exchanger to be improved, and the heat exchanger can have a certain level of heat exchange performance even when the heat exchanger includes no fins (finless heat exchanger). Since the finless heat exchanger includes no fins, the heat exchanger can be compact.
A finless heat exchanger including flat heat exchange pipes (heat exchanging portions) defining refrigerant flow paths, an entrance-side header to which an end of each heat exchange pipe is connected, and an exit-side header to which the other end of each heat exchange pipe is connected has been proposed as an existing finless heat exchanger (see, for example, Patent Literature 1). In the heat exchanger disclosed in Patent Literature 1, the flat heat exchange pipes are connected to the entrance-side header and the exit-side header so as to be arranged in the longitudinal direction of the entrance-side header and the exit-side header.